Canon
letter addressing the proper use of E-TTL speedlights (550EX and 420EX)

The EOS D30 has no sensor
to read flash illumination reflected from the CMOS during exposure.
If you want auto flash exposure through the lens, you must use
one of our EX-series Speedlites. Top of the line right now is
the 550EX, and we also offer 420EX, 220EX and Macro Ring Lite
MR-14EX. (We had a 380EX that was replaced recently by the 420EX.)
For more info on these products including specs, check out our
web site at:

http://www.usa.canon.com/camcambin/cameras/speedlite/550ex.html

...and go from there. You
can combine manual shutter speed and aperture settings with
auto flash exposure on the D30 together with any EX-series Speedlite,
and you won't have to dial down the flash exposure compensation
unless you're trying for a special effect.

* When the lens is set for
AF, E-TTL flash exposure is based primarily on the metering
zone covering the active focusing point.

* In the case of FEL with
the D30, flash exposure is always measured from the center of
the picture area, with a metering zone that roughly corresponds
to the partial metering circle in the viewfinder.

With these concepts in mind,
the next issue is how to determine the active focusing point.
The D30 offers 2 basic methods of focusing point selection:
manual and automatic.

* When the photographer
manually selects an individual focusing point, E-TTL flash exposure
remains linked to that point regardless of changes in composition
prior to exposure. This is why FEL is so valuable in 'focus
lock & recompose' scenarios.

* When the D30 is set for
automatic focusing point selection, the camera's algorithm for
selection varies according to the user-selected AF mode. When
One-Shot AF is combined with automatic focusing point selection,
the camera selects the closest readable subject. When AI Servo
AF is combined with automatic focusing point selection, the
camera expects the photographer to identify the main subject.
To do this, the outer focusing points are shut off at first.
Once the center focusing point has picked up a subject, the
outer focusing points are activated and the D30 is then able
to track subject movement from the center to the left or right
as well as from near to far or vice versa. When the D30 is set
for automatic focusing point selection in One-Shot AF or AI
Servo AF, E-TTL flash exposure tracks from point to point along
with the AF system.

It's obvious that no single
arrangement can work perfectly for every conceivable flash photo,
but the range of settings available do cover the vast majority
of typical shooting situations.

Here's an analysis of the
choices:

1. When you're working with
a still subject and there's plenty of time to set up the shot,
consider FEL as the best choice because it allows complete freedom
in composition under this situation.

2. For point-and-shoot simplicity
with stationary subjects, consider E-TTL set for One-Shot AF
together with automatic focusing point selection.

3. When you're working with
subjects moving laterally across the frame and you are using
flash, consider E-TTL combined with automatic focusing point
selection. This combination of settings allows the D30 to give
you as much assistance as possible in terms of placing maximum
metering sensitivity, at the active focusing point.

The choice of One-Shot AF
or AI Servo AF with automatic focusing point selection is up
to the photographer, but we would suggest trying both to get
a feel for how well they work in specific applications.

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Most of the reports we've
been hearing from D30 owners indicate that auto flash exposure
is very accurate with EX-series Speedlites including the 550EX,
420EX, 380EX, 220EX and MR-14EX as well as the built-in unit.

If you use any of these
Speedlites in E-TTL mode, one of the most important considerations
is ensuring that the subject you intend to meter is covered
by the active focusing point when the flash is metered.

In standard E-TTL flash
exposure mode, flash exposure is measured after the shutter
button is fully pressed but before the camera's reflex mirror
flips up. If you are using autofocus with the D30 and standard
E-TTL on the 550EX, you will therefore need to use the Focusing
Point Selector to cover your subject with the active focusing
point before and during the exposure.

If you have gotten into
the habit of locking focus using an individual focusing point,
and then recomposing before the shot, you will almost certainly
get a bad flash exposure in E-TTL mode with the 550EX or any
other EX-series Speedlite. This is because the active focusing
point is usually positioned over the background during exposure.
There is a workaround, called "Flash Exposure Lock,"
or FEL for short. This feature allows the camera to memorize
the flash meter reading from the D30's spot metering pattern
by preflashing the subject using the AE lock button. Once this
has been done, then recompose and shoot.

For details on both of these
methods (E-TTL and FEL), please refer to your D30 User's Guide,
Chapter 4.

You may find that you prefer
slightly more or less fill than the 550EX provides at its default
settings. If so, adjust the Flash Exposure Compensation setting
and take some test shots using the LCD monitor to judge the
results. We would also suggest that as a general rule of thumb,
you should set the D30's Custom Function 10 to C.Fn. 10-1 at
all times. This will put you in complete control of the flash
exposure compensation setting and help to make your results
more consistent and predictable, especially in outdoor fill-flash
situations. Once again, this topic is covered thoroughly in
the D30 User's Guide.

E-TTL compares pre-flash
information with ambient metering data. It also uses the entire
sensor for flash metering. Maximum emphasis is normally placed
on the metering zone nearest the active focusing point, but
that metering zone is considerably larger than the focusing
point alone. It's also possible to get an "averaged"
E-TTL flash meter reading by switching the lens to manual focus
mode.